Sibling relationships are an important contributor to socioemotional development for normal children and those at risk for affective illness. In families with an affectively ill parent, sibling relationships can provide compensatory support, or serve as an additional source of relational stress. The nature of sibling interaction may also be related to the presence of child psychopathology. Observations of sibling interaction were made when the younger sibling was between 5-6 years of age and the older sibling was between 8-11 years of age, and again when the younger sibling was 8-11 and the older sibling was 12-16. The objective of the study is to examine patterns of interaction in the areas of affect, communication, and play behavior in these sibling pairs across the two developmental periods in terms of parental psychopathology, child disorders, and gender composition of the dyad. In addition, children's representations of the sibling relationship are considered.